Six companies in, Yianni Kellis has made early-stage the only stage he’s interested in.
A Pattern Built From Repetition
Most investors come to early-stage companies from one direction: they built something once, it worked, and now they write checks from a comfortable remove. Yianni Kellis got there a different way. He’s done it six times.
That track record, six founded companies, is the foundation of everything Kellis does now at Thinkk, the advisory and investment firm where he serves as Venture Partner. The focus is narrow by design: early-stage tech companies operating in finance and health, two sectors where the regulatory maze and trust deficit make the gap between a good idea and a working business especially hard to close.
“6x Founder & Venture Partner at Thinkk,” reads the bio on his X profile, alongside a self-described focus on AI, marketing, and global finance. The framing is deliberate. Kellis isn’t positioning himself as a generalist. He’s signaling a specific kind of operator experience, one that comes from having sat in the founder’s seat repeatedly and knowing where the floor usually falls out.
What Thinkk Actually Does
Thinkk operates at the intersection of capital and counsel. The firm advises early-stage founders, but the involvement doesn’t stop at a monthly call and a slide deck. Kellis invests alongside the advice, a structure that aligns his incentives directly with the companies he works with.
The target sectors aren’t arbitrary. Fintech and health tech share a common problem: high stakes for end users mean that trust has to be earned before growth can happen. A payments startup that fumbles compliance, or a health platform that mishandles data, doesn’t get a second chance at a first impression. The founders who navigate that pressure successfully tend to be the ones who had someone in their corner who had felt that pressure before.
That’s the value Kellis is selling. Whether the market agrees is a question answered deal by deal.
The Other Business: Building Brands for Builders
Running parallel to Thinkk is FameBoost, where Kellis focuses on personal brand development for founders, executives, and advisors. The logic connecting the two ventures isn’t hard to follow. If you’re going to advise early-stage companies on growth, you’d better understand how credibility is built from scratch, how an unknown name becomes a trusted signal in a crowded market.
FameBoost takes that understanding and productizes it. The clients aren’t celebrities. They’re operators who’ve realized that in a world where deals, talent, and capital often flow toward recognizable names, invisibility is a competitive disadvantage.
It’s worth watching how both firms develop together. A venture partner who can also sharpen how founders present themselves to the world is a different kind of offer than a check-writer alone.
A Life Lived Across Two Continents
Kellis splits his time between Chicago and Athens, Greece, a configuration that’s unusual enough to be worth noting, and meaningful enough to shape how he works. The Greek Orthodox Christian community is a meaningful part of his life, and his roots are evident in how he navigates between two very different professional cultures: the American startup ecosystem’s pace and the longer-relationship-cycle dynamics of European and Mediterranean business.
His father George and mother Maria, along with his three younger sisters, form the personal core around which the professional ambition orbits. That kind of grounding shows up, often enough, in how founders talk about what they’re actually building toward.
His Upwork profile offers a more transactional entry point for founders not yet ready for a full advisory relationship, a practical acknowledgment that not every collaboration starts with a term sheet.
The Credibility Question
Six companies founded is a number worth scrutinizing, not just citing. Repeat founders accumulate scar tissue along with pattern recognition, and the combination, when it’s real, produces a different quality of insight than any single successful exit. The question Kellis’s potential portfolio companies and clients will ask is simple: what did those six ventures actually teach him, and does the answer show up in the room?
The structure of Thinkk, advisory plus investment, narrow sector focus, Kellis’s own background as the primary differentiator, suggests he’s thought carefully about where that accumulated experience is most legible to the people who need it.
The founders who navigate early-stage pressure successfully tend to be the ones who had someone in their corner who had felt that pressure before.
For founders in fintech or health tech trying to get from idea to institution, that’s the pitch. Whether Kellis can deliver on it is what the next chapter of Thinkk will answer.
